This invention relates to an improvement of a method of connecting rubber or polyethylene insulation cables.
In the connection part of rubber or plastic (polyethylene, crosslinked polyethylene, etc.) insulation cables, after the conductors are connected, an internal semiconductive layer, a reinforcing insulation layer and, if necessary, an external semiconductive layer are formed on the conductor connection part in the stated order. Then, the cable connection part is heated under pressure so that the cable insulation layers and the reinforcing insulation layer form one unit. A method has been extensively employed to form the reinforcing insulation layer, in which the reinforcing insulation layer is formed by winding a tape of polymer material such as polyethylene, crosslinked polyethylene, or etylene-propylene copolymer or by pouring the same polymer material into a metal mold. Then it is heated under pressure to become integral with the cable insulation layers.
In one example of a conventional method of heating the reinforcing insulation layer under pressure, a vulcanized rubber tape is strongly wound on the reinforcing insulation layer to pressurize the latter, and under this condition it is heated by an electric heater or the like. However, the method is disadvantageous in the following respect. That is, when the vulcanized rubber tape is removed from the reinforcing insulation layer after heating, marks from the laps of the vulcanized rubber tape remain on the surface of the reinforcing insulation layer. Accordingly, it is necessary to polish the surface of the reinforcing insulation layer. Also, the reinforcing insulation layer is heated through the vulcanized rubber tape wound thereon and it takes a relatively long time to heat the reinforcing insulation layer.
In another example of a conventional method of heating the reinforcing insulation layer under pressure, the reinforcing insulation layer is heated and shaped by using the metal mold, when used for forming the reinforcing insulation layer by pouring the polymer material thereinto. In the method also, the marks of the joint of the metal mold remain on the surface of the molded reinforcing insulation layer. Therefore it is necessary to polish the surface of the reinforcing insulation layer.
In the case where, in connecting cables, it is necessary to provide the external semiconductive layer on the reinforcing insulation layer, the following method has been employed. That is, after the reinforcing insulation layer is heated under pressure, the surface thereof is polished to be smooth. Thereafter, a semiconductive tape is wound on the reinforcing insulation layer and is then heated to provide the external semiconductive layer. Therefore, it takes a longer time to achieve cable connection.